Fire extinguisher

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A fire extinguisher is a device that puts out small fires in emergency situations. They are commonly available at most hardware stores. In the lab, almost every possible type of fire (solid and liquid combustibles, electrical fires, oil fires, and most commonly, metal fires) may occur, so it is good to be prepared

Types of fire extinguishers

No fire extinguisher works on all types of fires. Using an extinguisher that is not rated for the type of fire being fought can have various effects on the fire, from doing absolutely nothing at all to spreading the fire or causing an explosion.

The most common fire extinguishers are red and are rated for the three most common types of house fires: combustible solids (paper, wood, plastics), combustible liquids (gasoline, motor oil, diesel fuel) and electrical fires. These extinguishers will work with most types of fires, but cannot be used on metal fires.

The classification of fire extinguishers is complex and even varies from country to country.

Classification by class

  • Class A: Used for fires from common materials, such as wood, paper, fabric, cotton and most kinds of trash, including plastic.
  • Class B/C: Used for fires whose fuel is a combustible solid, liquid or gas. The US system designates all such fires "Class B". In the European/Australian system, flammable liquids are designated "Class B", while burning gases are separately designated "Class C". Halon and CO2 are used as extinguishing agents.
  • Class C or Class E: Used for electrical fires, fires started in or near electrical equipment. The US system designates these "Class C"; the Australian system designates them "Class E". In Europe, "electrical fires" are no longer recognized as a separate class of fire as electricity itself cannot burn. The items around the electrical sources may burn. By turning the electrical source off, the fire can be fought by one of the other class of fire extinguishers. This sort of fire may be caused by short-circuiting machinery or overloaded electrical cables. Carbon dioxide and dry powders are used.
  • Class D: Class D fire extinguishers consist of combustible metals such as alkali metals, alkali-earth metals, lanthanides, titanium, and zirconium. The most common of extinguishing agents are sodium chloride granules and graphite powder. In recent years, powdered copper has also come into use.
  • Class K or Class F: Class K fire extinguishers are used for fires started from unsaturated cooking oils as well as other types of flammable liquids with a high flash point. Fires that involve cooking oils or fats are designated "Class K" under the American system, and "Class F" under the European/Australasian systems. Watermist can be used to extinguish such fires, but NEVER liquid water, as it will cause an explosion. Recently a mixture of water and starch was found to be effective at extinguishing transformer oil fires. Powders and CO2 are commonly used as fire extinguishing agents.